Cover plate for a domestic appliance, said cover plate comprising a fabry-perot interference layer

ABSTRACT

A cover plate for a domestic appliance includes a support plate made of a glass or glass ceramics and having at least one at least partially transparent area for covering a display element. A coating is applied onto the support plate and includes at least one semi-transparent metallic layer having a layer thickness between 10 nm and 50 nm, at least one further metallic layer, and a dielectric separation layer separating the further metallic layer from the semi-transparent metallic layer.

The invention relates to a cover plate for a domestic appliance having a support plate made of glass or glass ceramic with at least one at least partially transparent region for covering a display element and with a coating. A further aspect of the invention relates to a method for producing such a cover plate for a domestic appliance.

A domestic appliance cover plate having a metal-type layer is known from WO 2007/118744 A1. The metal-type layer covers decorative segments printed on the rear of the cover plate, to protect them.

A hob with a glass ceramic plate is also known from DE 100 14 373 C2, having a metal-type coating. Such metal-type coatings are esthetically very pleasing, open up new possibilities for domestic appliance design, and in particular allow glass ceramic cover plates to have a metallic appearance, with the result that their overall impression can be matched to metal parts of the domestic appliance. For example in the case of a hob, a glass ceramic cover plate can have an appearance of stainless steel, which fit particularly harmoniously into a kitchen with stainless steel components.

A cover plate for a hob is known from US 2008/0264931 A1, being coated with a semi-transparent metallic layer. The semi-transparent metallic layer can be applied in addition to a colored layer to produce a metallic shine.

The object of the present invention is in particular to extend the configuration options for generic cover plates. A further object of the invention is to provide a method for producing such a cover plate.

The objects are achieved in particular by a domestic appliance cover plate as claimed in claim 1 and by a method as claimed in claim 15. Further advantageous embodiments and developments of the invention will emerge from the subclaims.

The invention is based in particular on a domestic appliance cover plate having a support plate made of glass or glass ceramic with at least one at least partially transparent region for covering a display element and with a coating.

It is proposed that the coating comprises at least one semi-transparent metallic layer with a layer thickness between 10 nm and 50 nm and at least one further metallic layer, which is separated from the semi-transparent metallic layer by a dielectric layer. In the cited range of layer thicknesses the coating goes from being sufficiently transparent to allow illuminating elements, for example display elements such as light-emitting diodes or 7-segment displays, to shine through and also to produce a metallically reflecting surface, in particular when the display element is switched off. With layer thicknesses below 10 nm the transparency is too great and no longer allows the coating to appear metallic, while with layer thicknesses above 50 nm the transparency is no longer sufficient to allow display elements and/or heating elements that glow red to shine through. Of particular advantage is a transmission of 30%-80% for red light with a wavelength of 700-800 nm. Providing a further metallic layer means that light let through by the semi-transparent layer can be reflected and can interfere with the light let through in the dielectric layer. This produces a particularly impressive, shimmering surface, which opens up new design possibilities. The thickness of the dielectric layer can in particular be less than 800 nm. This puts the layer thickness in the range of visible light, resulting in interesting interference effects between the light components reflected by the different metallic layers. The interference effects can be utilized to produce an iridescently shimmering surface and/or selected so that certain color components are absorbed and the reflected light takes on a certain color. In particular distances of less than 500 nm can be selected for this purpose.

The inventive domestic appliance cover plate can be used in many different fields. For example the cover plate can be used as a hob cover plate for a hob, in particular an induction hob or radiant hob, or as the front panel of a domestic appliance door, for example of an oven, microwave oven or steam cooker. It could also be used in refrigerators, dishwashers, washing machines and tumble dryers. The advantages of the invention come to bear in particular when touch sensors are also disposed behind the cover plate along with display elements, forming a user interface of a domestic appliance. The metallic look can then be perfected so that when the domestic appliance is inactive the user interface disappears almost completely behind the reflecting metal layer. When the domestic appliance is active, light-emitting elements of the user interface can be activated, which then shine through the partially transparent metallic layer.

Damage to or corrosion of the metallic layer can be prevented if it is applied to a rear face of the support plate facing the display element and/or if it is covered by a dielectric protective layer.

Particularly interesting effects can be achieved if the cover plate comprises at least two at least partially transparent metallic layers, the layer thickness of which can be in particular in the above-mentioned range of 10 nm to 50 nm. These can be separated from one another by a dielectric layer, the thickness of which can be in particular between 5 nm and 500 nm, preferably between 10 nm and 100 nm.

A capacitive touch sensor system can be achieved, if at least one of the metallic layers features a break in proximity to a region for covering a touch sensor for the electrical isolation of the region. The touch sensor is then not screened by the entire coating, which acts as a large-surface electrode but just by a small region of the coating defined and isolated by the in particular linear break, it being possible also for said coating to be completely absent in proximity to the touch sensor. The break can also prevent inductive sensors being screened by the coating.

Disruption of the generally metallic impression by large, black-looking windows can be avoided, if the metallic layer is interrupted along lines with a width of less than 2 mm, in particular less than 0.2 mm. The break can be produced in particular by cutting into the metallic layer. To this end the metallic material can be removed by a laser for example to produce the break. Even breaks with a width of less than 1 mm can thus be produced simply and economically.

Further configuration possibilities can be opened up, if the domestic appliance cover plate comprises a marking layer printed on at least parts of the support plate. The marking layer can be printed on the rear face of the support plate in particular using a screen printing procedure or an inkjet printing procedure. In one particularly advantageous embodiment of the invention one or both metallic layers are applied to the support plate after the marking layer has been printed on.

The metallic layer can be used as a conductor track and/or control electrode, if the domestic appliance cover plate comprises at least one contact electrode connected to the metallic layer to feed control signals into the metallic layer.

Metallic layers with a precisely defined layer thickness can be produced for example by means of physical vapor deposition PVD. The procedure is characterized in particular by gas production by the particles forming the layers, the transportation of the vapor to the substrate and the condensation of the vapor on the substrate for the purpose of layer formation. Iron, steel, copper or a suitable alloy such as silicon with aluminum can be selected as the metal materials for the metallic layer. A silicon dioxide layer can be provided between the support plate and the metallic layer, possibly also resulting from the natural oxidation of the surface of the support plate.

Configuration freedom can be further improved if the support plate and/or the coating comprises internal laser engraving.

Further corrosion protection can be achieved if at least an outer layer of the metallic layers is covered by a dielectric protective layer.

In possible embodiments at least one of the metallic layers is made from a material selected from the group consisting of silver (Ag), gold (Au), aluminum (Al), molybdenum (Mo), copper (Cu), nickel (Ni), silicon (Si), stainless steel (SSt), titanium (Ti), niobium (Nb), tantalum (Ta), tungsten (W), palladium or an alloy or mixture of two or more of these metals.

A black shimmering layer can be achieved, if a Ni—Cr alloy with 80% nickel and 20% chromium is used.

Oxides selected from the group consisting of stannic oxides, zinc oxides, aluminum oxides, titanium oxides, silicon oxides, nickel oxides, chromium oxides, niobium oxides, tantalum oxides or mixtures thereof and/or nitrides of metallic elements selected from the group consisting of silicon nitrides, titanium nitrides, chromium nitrides and aluminum nitrides or mixtures thereof have proven advantageous as the material for at least one of the dielectric separation layers.

A further aspect of the invention relates to a method for producing a cover plate of the type described above.

Further advantages and features of the invention will emerge from the description of the drawing which follows. Exemplary embodiments of the invention are illustrated in the drawing. The drawing, description and claims contain numerous features in combination. The person skilled in the art will expediently also consider these features individually and combine them in meaningful further combinations. In the drawing:

FIG. 1 shows a top view of a hob with a cover plate, a display element and a number of operating elements,

FIG. 2 shows a schematic sectional view of the cover plate according to FIG. 1,

FIG. 3 shows a domestic appliance cover plate according to a further embodiment of the invention with two metallic layers,

FIG. 4 shows a domestic appliance cover plate according to a further embodiment of the invention with three metallic layers, and

FIG. 5 shows a sectional view of a domestic appliance cover plate according to a further embodiment of the invention with internal laser engraving.

FIG. 1 shows a hob with a cover plate, which comprises a printed support plate 10 made of glass or glass ceramic. Various markings 12 are printed on the rear face of the support plate 10 facing away from the visible face of the support plate 10, it being possible to see these through the glass ceramic material of the support plate 10.

The markings 12 are applied using a screen printing procedure and mark heating zones 14 a to 14 d of the hob and the elements of a user interface 16 in a known manner.

The user interface 16 comprises a display element 18, shown for simplicity here as a 7-segment display, having a number of light-emitting diodes 20 (FIG. 2). Once the markings 12 had been printed on, in a production procedure for producing the inventive domestic appliance cover plate a coating 24 was applied to the rear face of the support plate 10, comprising a number of metallic layers 22 a-22 c (FIG. 3), the layer thickness of which is between 10 nm and 50 nm. In the exemplary embodiment illustrated in FIG. 1 the coating 24 (FIG. 2) comprises a stainless steel layer and a copper layer, which were produced using physical vapor deposition.

FIG. 2 shows a sectional view of the cover plate from FIG. 1. The sectional view is highly schematic. The size ratios in particular are greatly distorted. The support plate 10 is printed on its rear face with a serigraphically produced marking 12 and then coated with a coating 24, produced using a sputter or PVD procedure.

FIG. 3 shows a sectional view of the layer structure of the coating 24. Applied to a silicon dioxide layer (not shown here) on the rear face of the substrate of the support plate 10 are first a first metallic layer 22 a of iron/stainless steel, then a dielectric separation layer 32 with a thickness D between 10 and 100 nm and then a second metallic layer 22 b of copper, which is protected from damage by a dielectric protective layer 26. The thickness of the metallic layers 22 a, 22 b is between 10 nm and 50 nm, preferably between 20 nm and 40 nm, while the thickness of the protective layer 26 is several 100 nm.

Disposed behind the cover plate or support plate 10 is a light-emitting diode 20 (FIG. 2) of the display element 18, the light of which can be perceived through the metallic layers 22 a, 22 b, the separation layer 32, the protective layer 26 and the support plate 10 from the visible side of the support plate 10.

Since the metallic layers 22 a, 22 b are applied to the support plate 10 after the marking 12, the metallic layers 22 a, 22 b also cover the marking 12 when viewed from the rear of the support plate 10. Alternatively one of the metallic layers 22 a, 22 b and/or the separation layer 23 can have cut-out sections, which can be established for example using a mask. These layers can then take over the role of the marking 12, which is no longer necessary.

The metallic layers 22 a, 22 b have been removed along a linear break 30 by laser processing. The region 38 of the coating 24 directly above the touch sensor 28 and in its immediate vicinity is therefore isolated electrically from the other parts and is not connected in an electrically conducting manner to other parts of the metallic coating 24. The width of the gap forming the break 30 is in the region of less than 0.2 mm, so that from the visible side of the support plate 10 anyway the break 30 is visible as a very thin line, while the remainder of the cover plate has a continuous surface with a metallic appearance in the region of the touch sensor 28.

The metallic layers 22 a, 22 b are semi-transparent so the entire surface of the cover plate forms a partially transparent region 40.

The small thickness of the metallic layers 22 a, 22 b on the one hand ensures sufficient transparency so that the light from the light-emitting diode 20 can shine through the coating 24. On the other hand the metallic layers 22 a, 22 b reflect the incident light through the support plate 10 in such a manner that when the light-emitting diode 20 is inactive, only the continuous layer 22 can be seen. The cover plate therefore acts in the manner of a semi-transparent mirror.

The components of the light reflected by the rear metallic layer 22 b interfere with the components of the light reflected by the front metallic layer 22 a. This interference produces an interesting shimmering surface.

FIG. 4 shows a sectional view of an inventive domestic appliance cover plate according to an alternative embodiment of the invention, in which the coating 24 comprises three metallic layers 22 a, 22 b, 22 c. The different layers 22 a to 22 c are separated from one another by dielectric separation layers 32 a, 32 b and the outer metallic layer 22 c is enclosed by a protective layer 26. The dielectric separation layers 32 a, 32 b have a layer thickness that produces desirable and controlled interference between the components of the incident light through the support plate 10 reflected by an upper layer 22 a on the one hand and the components of the light reflected by a lower layer 22 b, 22 c on the other hand. This allows a metallically shimmering, iridescent surface to be achieved.

Examples of possible layer sequences are glass, iron or steel and titanium nitrite to produce a steel-like color, glass, silicon dioxide, copper, silicon dioxide, iron (steel) and silicon dioxide for a red shimmer, glass, silicon dioxide, a silicon-aluminum alloy (SiAl), silicon dioxide, iron (steel) and silicon dioxide for a yellow color and glass, silicon dioxide, iron (steel), silicon dioxide, iron (steel) and silicon dioxide in different layer thicknesses for a bluish or grayish coloring.

The protective layer 26 made of titanium nitrate is particularly robust. The protective layer 26 serves among other things to prevent oxidation of the metallic layer 22 at high temperatures.

Electrical switching circuits can be engraved in the different metallic layers 22 a to 22 c with the aid of a laser and the metallic layers 22 a to 22 c can be provided with contact elements (not shown here), in order to be able to use the metallic layers 22 a to 22 c as conductors for transmitting control signals or the like.

In the exemplary embodiments described above the separation layers 32, 32 a, 32 b can be made of oxides of tin, zinc, titanium, aluminum, silicon, tantalum, niobium, nickel, chromium or mixtures thereof and/or of nitrides of titanium, silicon, aluminum, nickel, chromium or mixtures thereof.

FIG. 5 shows a further alternative exemplary embodiment of the invention, in which the support plate 10 and the coating 24 are equipped with internal laser engravings 36.

REFERENCE CHARACTERS

-   10 Support plate -   12 Markings -   14 a Heating zone -   14 b Heating zone -   14 c Heating zone -   14 d Heating zone -   16 User interface -   18 Display element -   20 Light-emitting diode -   22 a Layer -   22 b Layer -   22 c Layer -   24 Coating -   26 Protective layer -   28 Touch sensor -   30 Break -   32 Separation layer -   32 a Separation layer -   32 b Separation layer -   36 Internal laser engraving -   38 Region -   40 Region -   D Thickness 

1-15. (canceled)
 16. A domestic appliance cover plate, comprising: a support plate made of glass or glass ceramic and having at least one at least partially transparent region for covering a display element; and a coating applied onto the support plate and comprising at least one semi-transparent metallic layer having a layer thickness between 10 nm and 50 nm, at least one further metallic layer, and a dielectric separation layer separating the further metallic layer from the semi-transparent metallic layer.
 17. The domestic appliance cover plate of claim 16, wherein the semi-transparent metallic layer is applied to a rear face of the support plate facing the display element.
 18. The domestic appliance cover plate of claim 16, further comprising at least two of said at least partially transparent metallic layer, and a further dielectric separation layer separating said at least two of said at least partially transparent metallic layer.
 19. The domestic appliance cover plate of claim 18, wherein the further dielectric layer has a thickness of less than between 5 nm and 500 nm.
 20. The domestic appliance cover plate of claim 16, wherein at least one of the metallic layers has a break in proximity to a region for covering a touch sensor for electrical isolation of the region.
 21. The domestic appliance cover plate of claim 20, wherein the break is produced by cutting into the metallic layer.
 22. The domestic appliance cover plate of claim 16, further comprising a marking printed on at least parts of the support plate.
 23. The domestic appliance cover plate of claim 22, wherein at least one of the metallic layers is applied to the support plate after the marking has been printed on.
 24. The domestic appliance cover plate of claim 16, further comprising at least one contact electrode connected to at least one of the metallic layers to feed control signals into the metallic layer.
 25. The domestic appliance cover plate of claim 16, wherein at least one of the metallic layers is applied to the support plate using a PVD sputter procedure.
 26. The domestic appliance cover plate of claim 16, wherein one of the metallic layers defines an outer metallic layer which is covered by a dielectric protective layer.
 27. The domestic appliance cover plate of claim 16, wherein at least one of the metallic layers is made from a material selected from the group consisting of silver, gold, aluminum, molybdenum, copper, nickel, silicon, stainless steel, titanium, niobium, tantalum, tungsten, palladium, an alloy, and a combination of two or more of these materials.
 28. The domestic appliance cover plate of claim 16, wherein the dielectric separation layer is made of at least one material selected from the group consisting of oxides and nitrides of metallic elements.
 29. The domestic appliance cover plate of claim 28, wherein the oxides are selected from the group consisting of stannic oxides, zinc oxides, aluminum oxides, titanium oxides, silicon oxides, nickel oxides, chromium oxides, niobium oxides, tantalum oxides, and combinations thereof.
 30. The domestic appliance cover plate of claim 28, wherein the nitrides of metallic elements are selected from the group consisting of silicon nitrides, titanium nitrides, chromium nitrides aluminum nitrides, and combinations thereof.
 31. The domestic appliance cover plate of claim 16, wherein the support plate comprises at least one marking in the form of an internal laser engraving.
 32. The domestic appliance cover plate of claim 16, wherein at least one of the metallic layers is removed again from parts of the support plate to produce structures. 